The horse is an animal which has changed greatly due to man's intervention in its evolution. When horses were bred for various performance characteristics other, less desirable characteristics were also inherent in the changes. Among these detrimental (at least from the standpoint of foot health) introductions are a reduction of the size of the feet of certain horse breeds and an alteration of the angle of inclination from the leg to the foot in others. Furthermore, the treatment of domestic horses has altered the manner in which the horse lives, runs, reproduces and eats. All of these changes have resulted in special problems occurring in the horse's feet.
Wild horses rarely suffer from lameness unless they are injured in some way. This is true mainly due to the fact that they constantly run on uneven ground, stand in water and otherwise are exposed to environmental factors which wear away the hoof material in the manner in which God and nature intended. Domestic horses are not so lucky. Domestic horses are exposed to much less uneven terrain and spend a great deal more time standing around than wild horses. They are protected from the more harsh and abrasive aspects of nature. Furthermore, special feeds which create other desirable conditions in domesticated horses may have a deleterious effect on the feet. Therefore, it has long been recognized that special care is required to maintain domesticated horses' feet in proper condition. Horseshoes have been the main devices used for this purpose.
A good discussion of some of the problems relating to the feet of horses may be found in the publication entitled The Illustrated Veterinary Encyclopedia for Horsemen put out by Equine Research Inc., 1977 edition, especially in chapter 2. As the authors point out, there is a difference between the "foot" and the "hoof". Contrary to common usage, the hoof is not a term properly applicable to the entire foot but is technically restricted to that portion which no longer constitutes living tissue. Predominantly, what most folks call the hoof wall is really the hoof and what is commonly designated the hoof is, in reality, the foot. In Applicant's earlier filed application entitled "A Cushioned Horseshoe", Ser. No. 619,616, the common nomenclature was utilized. However, although the present invention is a modification of, and closely related to, the invention disclosed in the Cushioned Horseshoe application, the more technically correct language has been adopted for the present application.
Two other publications which have dealt with the issue of lameness in horses caused by defects or injuries to the feet and hooves are the books "THE LAME HORSE, CAUSES, SYMPTOMS & TREATMENT" by Dr. James R. Rooney and "LAMENESS IN HORSES" by O. R. Adams. These references, as well as the Encyclopedia, provide a great deal of discussion of the problems encountered by horses with hoof injuries or defects. The special problems known as "toe-in" and "toe-out", which are related to foot conformation, are dealt with in the Encyclopedia at pages 39 to 42; in Rooney at page 135 and following; and in Adams at pages 404 to 410. The problem of navicular disease or damage is discussed in the Encyclopedia at pages 69 to 74; in Rooney at pages 121 to 130; and in Adams at pages 260 to 276 and 413, while that cause of lameness commonly known as laminitis or "founder" is discussed in the Encyclopedia at pages 59 to 66; in Rooney at pages 130 to 134; and in Adams at pages 247 to 259.
A further extensive discussion of navicular disease is found in an entire issue of Equus magazine, June 1984, a special section of which is devoted to various articles relating to the navicular bone and the maladies which affect it. An article beginning on page 48 outlines the importance of blood circulation to navicular function and illustrates the problems that occur when circulation is restricted. This article reflects the common opinion that once navicular disease becomes established it is not possible to reverse its effects.
Another useful reference which includes a good layperson's description explaining the relationship of the various elements of the horse's foot was published by Equus Magazine in Volume 56, pages 34 to 43. The article, entitled "Ingenious Engineering, the Secrets Behind Those Successful Steps" by Emily Kilby with Douglas Leach, PhD., deals with the manner in which a horse's foot operates and with the effect of the environment upon that operation.
From the above publications it may be understood that the bottom surface of a horse's foot includes two significant areas. The exterior rim of the hoof is a horn-like material called a "hoof wall." The hoof wall is analogous to a human fingernail. The inner portion of the bottom foot surface is more recently living material. This area, called the sole, is more analogous to the callous on a finger and is directly continuous with living soft tissue, unlike the hoof wall which has buffering connectors separating it from soft tissues. In normal running the major impact on the shod horse's foot is absorbed through the hoof wall, or horn-like portion, while the sole absorbs only a slight amount, if any, of the impact. This is particularly true on hard ground. On soft ground with an unshod horse, however, the hoof wall actually digs into the turf to a certain degree and the interior sole will directly contact the surface of the ground. This contact is important to proper operation and circulation in the hoof.
The interior of the hoof includes both bone structures and soft tissues. The lowermost bone is the coffin bone which is supported and hinged at its rearmost portions by the distal sesamoid bone, usually called the navicular bone. The deterioration of the navicular bone, caused by disease or injury, is nearly always critically crippling to the horse. Some sources indicate that the initial injury actually occurs in the tendons and cartilage associated with the navicular bone but the net result is great harm to the horse. Commonly attributed causes are improper heel height, genetic malformation and overly hard running surfaces. Navicular problems are particularly prevalent in jumping horses.
It has long been considered that shoeing horses helps to lessen the effect of impact of the foot on hard ground or such surfaces as race tracks and performance rings. Therefore, numerous developments and inventions have been made in the field of horseshoes. In many cases the object of the shoe has been to attempt to reduce the incidences of lameness.
One area of invention in the horseshoe field has specifically related to attempting to cushion the impact by the use of flexible and shock-absorbing materials as a part of the horseshoe. This has been thought to reduce the opportunity for foot injury and thereby to limit lameness.
Examples of attempts to make cushioned horseshoes are described in U.S. Pat. No. 62,867, issued to D. L. McDonell on Mar. 12, 1867; U.S. Pat. No. 308,449 issued to W. V. Wallace on Nov. 25, 1884; U.S. Pat. No. 371,789 issued to A. W. Robertson on Oct. 18, 1887; U.S. Pat. No. 546,145 issued to H. H. Gibbs on Sept. 10, 1895; U.S. Pat. No. 620,878 issued to H. E. Bauer on Mar. 14, 1899; U.S. Pat. No. 3,288,223 issued to D. Ferguson on Nov. 29. 1966; U.S. Pat. No. 3,200,885 issued to L. R. Johnson on Aug. 17, 1965; U.S. Pat. No. 3,603,402 issued to R. McDonnell on Sept. 7, 1971; and British Pat. No. 1584-339 issued to D. J. Brown on Feb. 11, 1981. Each of these references discloses a horsehoe intended to cushion the impact on the horse's hoof wall and thus improve the lifetime of the hoof.
Some attempts have also been made which provide some special support to the heel and frog portions of the hoof. These include a continuous rubber pad such as that shown in FIG. 1 of U.S. Pat. No. 1,690,365 issued to R. E. Fruin on Nov. 6, 1928 and a heel spring device such as disclosed in U.S. Pat. No. 648,236 issued to A. H. Bush on Apr. 24, 1900. However, even in these patents the frog support was merely a byproduct of ulterior purposes. Apparatus adapted to put direct pressure on the frog and the heels is shown in Adams at pages 411 and 412 (FIGS. 9-15 and 9-17). This device is used to correct problems with the frog and is not directly applicable to toe-in, toe-out, laminitis and navicular problems.
A further commercially available flexible type of horseshoe, being of a one-piece flexible plastic material, is known as the Coxton Poly-shoe. This shoe has been made the subject of U.S. Pat. No. Des. 230,234.
The prior art horseshoes have all been directed at protecting the hoof wall portion of the foot. All are directed to impact the outline of the hoof only, with some rare attention to the frog, and not to relate to the entire area of the lower surface of the foot. The forward portion of the sole, especially, has been ignored. Thus, the prior art horseshoes do not act to spread impact throughout the sole portion of the hoof as well as the hoof wall. The net result of this is that the natural impact heel spreading and circulation pumping action of the hoof is not properly enabled by prior art horseshoes. None of the prior art methods accurately reproduce the conditions of an unprotected hoof on natural terrain in conjunction with their meritorious effects on protecting the hoof wall against unnatural terrain. Furthermore the prior art attempts are not directed at reversing the damage, once it has occurred, or in providing therapeutic effects to the lame horse.